Soil acidity is managed by land use, depending on aluminium concentration. In high Al soils: shifting cultivation in forest systems using slash-and burn practices, short term tuber and root crops cultivation in natural post-forest pastures, tea plantations, etc. In low Al soils: very more possibilities by regular liming.

Thank you Dr. Opdecamp for your response. Do you mean shifting cultivation as a part of management practices in high Al soils. if so, then why? your response really interests me.

See multiple uses of charcoal and biochar: many books and articles on the subject have been published (see Glaser, Lehmann, and others as authors). The use of charcoal for the improvement of tropical acid soils (poor in organic matter and rich in Al) has been suggested as a mean to add stable carbon with strong sorption and exchange properties. The model is "Terra preta do Indio" from Amazonia, known to have supported sedentary agriculture in Pre-Colombian times, thanks to the use of charred plant material as both a source of black carbon and a fertilizer. Pantropical peregrine earthworms such as Pontoscolex corethrurus are suspected to play an a role in the disintegration and incorporation of charcoal to the mineral part of the soil (see several articles by Topoliantz and Ponge).

There has been a general thumb rule in crop cultivation... Grow acid crops in alkaline soils and alkaline crops in acid soils... Initiate growing alkaline crops and at the same time addition of manure and as suggested charcoal and biochar etc... these things can assist in production. Earthworms like Octochaetona serrata prefer acidic soils and may get attracted with suitable remediation. These earthworms are capable of creating neutral micro-niches. I feel crops like ragi though may initially yield less would be suitable for these soils. If properly managed with green manure incorporation, manure addition and with charcoal and biochar integrated approach, it could be possible.

Citric fruits like lime etc grow better in slightly alkaline soils and alkaline crops like ragi grow well in acidic soils...

Burning vegetation, especially forest, provides ashes like CaO and MgO which neutralize Al. Unfortunately, Al neutrazitation is only temporary: a few years. This short time is due to the fact that Aluminium doesn't prepicitate in Al(OH)3 but only polymerise in Al-OH amorphous species. Amorphous Al-OH polymers depolymerize with continuing acidification caused by soil and root respiration and by nitrification. The same process happens with liming these Al-soils.

Para este tipo de suelos, considero importante efectuar un encalado periódicamente para neutralizar la acidez del Al intercambiable a pH 5,5 y mejorar la disponibilidad de nutrientes como nitrógeno, fósforo y bases cambiables. Esto aumentará la producción de cultivos como Té, Yerba mate, Citrus, Mandioca, Tabaco, forestales que se adaptan bien a condiciones ácidas.

Es fundamental calcular bien la necesidad en cal en base al contenido de Al intercambiable, para no sobreencalar el suelo.

As though there is still a tendency in some quarters to correct the acidity by liming and existrencia variable charge is ignored. Furthermore rule is taken as it exists only inferirtes to pH 4.5. Unfortunately there is also lack of soil laboratories with quality control in many countries, giving reliable resultdos of Cation Exchange Capacity (CEC). An alternative could be this elavroar regional correlations with moisture to field capacity. This can be determined almost Colman columns in situ. .

An apology for the poor translation

As if there is still a tendency in some sectors to correct the acidity by liming and existrencia variable load is ignored. Besides, there is a rule that exists only at lower pH a.4 5 Unfortunately there is also lack of soil laboratories with quality control in many countries, with reliable results of cation exchange capacity (CEC). An alternative could be the development of regional correlations with moisture at field capacity. This can be determined almost Colman columns in situ. .

Dear Manoj,

since the problem of acid soil low fertility status has been known for long, many agricultural practices have been recommended to overcome the problem.

1) Large quantities are generally required to improve plant growth, and for many resource-poor farmers in the tropics carrying out semi-subsistence agriculture, its use is effectively prevented by the unavailability or the high cost of lime, or both

2) Use of Organic Waste Materials and wood ash

3) Wood ash –compost (please see my papers on the topic)

Co-composting organic wastes with wood ash as an additive to obtain a compost with higher liming potential and rich in nutrients is of great interest for both solving the problem of waste disposal and providing an economically attractive alternative to chemical fertilizers for acid tropical soils.

Our studies have showed that liming with gypsum or biochar or calcium-magnesia phosphate fertilizer is effective to alleviate soil acidity and improve soil structure. Moreover, as inorganic N fertilizer could acidify soil, therefore organic amendments could use to supplement soil fertilization.

Thanks to all for contributing to this discussion. But I feel the first part of my question is still unattended. Can anybody respond to: “what is the impact of soil acidity on global/regional food production in quantitative terms?” I mean if all the acidic soils in world are made to produce as capably as any healthy soil with optimum pH, what could be the yield advantage globally?

In Al-rich acid soils (more than 60% Al saturation), a population density of 10 inhabitants / km ² is relatively sustainable under shifting cultivation conditions and slash and burn practice. These soils are mostly part of a forest system than of a crop system!

Dear Dr Mendonca, I do agree with you that Brazil has managed to produce enough food by efficient management of acidic soils. Sadly in India, crop productivity in acid soil regions, particularly in northeast India, is lagging far behind the national average productivity. could you please advice some relevant literature (any review if possible) on extent, distribution and management of soil acidity for crop production in Brazil.

It is not easy to reply the first question. When soil pH>5.5, most of plants can grow well. But for stongly acid soils, the reduction in crop yield depends on soil acidity and fertility and vary with plant kinds. Because some plants are more sensitive to soil acidity, especually Al toxicity.

Dear Dr. Ren-Kou Xu: I do realize that quantitative response to the first part of question is difficult. but I was tempted to know if any global estimate on that aspect is available. By the way, could you please share your view on the extent of soil acidity in china, and status of crop productivity on acidic soils vis-à-vis normal pH soils. any relevant literature on this?

Thanks

You may read the following paper to know the extent of soil acidity in China: Guo JH, Liu XJ, Zhang Y, Shen JL, Han WX, Zhang WF, Christie P, Goulding KWT, Vitousek PM, Zhang FS. 2010. Significant acidification in major Chinese croplands. Science, 327: 1008-1010. But I have not information on crop yields.